Control system for resistance welding

• US 4,387,289 A
• Filed: 07/27/1981
• Issued: 06/07/1983
• Est. Priority Date: 08/11/1980
• Status: Expired due to Fees

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Kawaguchi, Yoshio, Nakata, Shuji, Nishikawa, Masahiro
• Primary Examiner(s): Shaw, C. C.
• Application Number:
  US06/287,178
• Time in Patent Office: 680 Days
• Field of Search: 219/108, 219/109, 219/110, 219/114, 219/115, 219/117.1
• US Class Current: 219/110
• CPC Class Codes: B23K 11/252 using digital means

Abstract

A system for resistance welding in which the welding voltage between the electrodes is controlled by changing the pressure applied to the electrodes or the firing phase angle of the welding current in accordance with a reference voltage curve or a reference voltage integration curve. The system comprises a voltage sensor, a reference voltage generator, a differential amplifier, and a pressure control device, or a calculating unit for determining an appropriate firing phase angle of the welding current. The system thus improved can ensure a stable, good welding quality, since the welding voltage is always controlled by a series of optimum welding voltages, during the welding process, in accordance with a reference voltage curve with respect to time, preferably in terms of cycles of the welding current.

Claims

1. A control system for welding, which comprises:

(a) a voltage sensor for detecting the voltage V_c between a pair of welding electrodes between which members to be welded are pinched while a welding current is flowing;

(b) a base voltage presetting circuit for previously setting a desired base voltage V_o ;

(c) an integrator for integrating the difference between the voltage V_c detected by said voltage sensor and the base voltage V_o preset in said base voltage presetting circuit with respect to welding time only when each half-wave peak valve of the detected voltage V_c exceeds the base voltage V_o ;

(d) a reference voltage generator for generating a series of predetermined reference welding voltages based on a reference voltage integration curve with respect to welding time;

(e) a differential amplifier which compares the voltage V_c detected by said voltage sensor with the voltage based on the reference voltage integration curve and outputs a control signal V_d in response to the difference between the two voltages;

(f) a current controller for controlling the welding current in the manner of firing phase angle;

(g) a current sensor for detecting the welding current from said current controller;

(h) a memory for storing initial firing phase angle values and for storing the preceding firing phase angle of the welding current detected by said current sensor; and

(i) a calculating unit for calculating an appropriate firing phase angle depending on an output signal V_d from the differential amplifier and a signal from said memory and for outputting the calculated result to said current controller;

whereby the welding voltage between the electrodes is controlled by changing the firing phase angle of the welding current, in accordance with the predetermined reference voltage integration curve, so as to obtain a stable welding quality.

2. A control system for welding as set forth in claim 1, which further comprises:

(a) a peak voltage holding circuit for holding each half-wave peak value of the detected voltage for a half cycle, disposed between said voltage sensor and said integrator; and

(b) a current-time controller for outputting a start-stop signal to said current controller and for outputting a start signal T_p to said reference voltage generator, said memory, and said voltage peak-value holding circuit,

whereby the system is controlled with a time delay at the start so as to prevent initial erroneous operation.

3. A control method of welding, which comprises:

(a) detecting the voltage V_c between a pair of welding electrodes between which members to be welded are pinched and through which an AC welding current is flowing;

(b) setting a base voltage V_o ;

(c) integrating the voltage difference between the detected voltage V_c and the base voltage V_o only when each half-wave peak value of the detected voltage V_c exceeds the level voltage V_o,

(d) generating a series of predetermined reference welding voltages based on a reference voltage integration curve with respect to time measured in cycles of the welding current;

(e) comparing the voltage difference between the integrated voltage and the predetermined reference voltage integration curve;

(f) detecting the welding current;

(g) storing the preceding firing phase angle of the detected welding current;

(h) calculating an appropriate firing phase angle depending on the voltage difference V_d between the integrated voltage and the predetermined reference voltage integration curve, and the stored preceding firing phase angle of the welding current; and

(i) controlling the welding current in accordance with the calculated results,

whereby the welding voltage between the electrodes is controlled, by changing the firing phase angle of the welding current, in accordance with the predetermined reference voltage integration curve so as to obtain a stable welding quality.

4. A control method of welding as set forth in claim 3, which further comprises:

(a) holding each half-wave peak value of the detected voltage for a half-cycle before comparison of the voltages;

(b) outputting a start-stop signal for synchronization;

(c) storing initial firing phase angles of the welding current for calculating the initial welding current; and

(d) correcting the reference voltage integration curve according to the detected firing phase angle.